NYONE with a small piece of wood, a
‘urzer, « couple of flazhlight batteries,
‘and $1.60 can build a modulated signal gen.
ferator that can be used to allga receivers
test rf civeutts, and do many ethor thingt
| modulated signel generator costirg 20 to
100'tamee az much ean do
How this inexpensive little signal source
can be made is shown in the Thotegraph
And wiring diagram: ‘Oniy five parts are
needed. ‘These are arranged om a pivce of
5. -thick plywood meaatiring shout 1” 6"
Gannections to the dry cells. are mado by
ining four brass wood screws Into the
hoard ori their Reals ire im contact sits
the brass cap on ono ead of the eell and ihe
bottom of the ‘ane cai on the other end
‘The sereats are spnced close enough to per
sit moderate pressure for geod elestmeal
contact. A simple bracket holds the ells
in place, Wires soldered to the slots the
serews connect the cells i-series and make
{he connections to the coil and buzzer.
‘The 0.25. fixed capacitor must be eon
nected, a5 thown, actos the buzzer com
tacts. IT this capacitor is connected across
‘the buzzer winding or across the buzzer a8
fwhola, the unit wil not operate,
‘The Miller 20-4." eoi) sm standard
bart which has been siightly modified. The
Crigiral coil has a primary winding eonsat~
Ing.of a few turns pf Pery fine wire wove
ona short adjustable sleeve. ‘This primary
The $1.60 Signal Generator
By FRANK H. TOOKER
Undoubtedly the simplest tunable
signal generator yet devised for
the novice ham and experimenter
—build it and see for yourself
will not be used so clip the fine wires tead-
Ing to i end remove the cardboard sleeve
by slipping it of tho end of the cell form
‘Wind on anew primary consisting of about
20 tums of ordinary No. 29 plastic hookup
‘wire over the hottom ond of the tuning eo
find connect the ends Wo the terminals trom
Which "the fine ‘wire primary Tears were
clifped, Loeate the parts on the board (the
‘at all critical), meke the
‘ctione shown in the A=
‘agram—and the unit Is fnised
How It Works
Tris a basic principe in electricity that
when a current flowing through a coll of
Wire especially one having an iron. core
such as the buzzer windlag—is sudteny
POPULAR ELECTRONICSInterrupted, a voltage much higher than
the battery voltage, sill appear momen.
larity across its terminals. ‘This induced
voltage is caused by the abrupt collapse of
the magnetic fald around the coil Use is
made of this rrineiple in tne present signal
generator
"A rapid suceassion of inductive voltage
kicks is induced arrest the buzzer winding
by the rapid making and breaking of the
Winding evrrent die to the operation of the
buzzer contaets..‘The current trom nese
voltage igcies Hows in sharp, rapid pulses
Through the primary cell, where t) exeites
the tunod circuit and eatses ito oncilate
Al'afrequoney: determined hy the eotting of
the yaniable eapacitor—in the present setup
ft any eained frequency between 540
and. 1700 ke. the standard broadesst band
‘Oscillations of the tuned circuit are aute-
matically modulated by the buzzer tone, £0
Al that is necessary when touting Un the
front end of an ace-de. Sct, for Instanes, Is
fa turn on the signal genorstor and set
its variable eapae:tor somewhere near the
high ene of the band. ‘Then tune the re
besver until the buzzer tone is heard corn
from the speaker. Adjust the trimmers on
the veasiver for loudest output, Conerally,
ro direct connection between tne. reser
And signal gencrator is needed. Standings
the two fairly clos together it sulleient
When tighter coupling 1s needed, wrap an
Insulated wire two or three turns around
the ead 10 one sie of the tained ees
‘sith the other end of the wice iyi near of
Connected to tho receiver loop of antenna
terminal
"The buzzor used in the generator shown
in the photograpn is TODD-eyee type gone
erally used for code practice, but a1 Ord
‘ae tesa |
Fetch ot shown in phe
apes 1785
rary household buzzer may be substituted
H necossary. 3n this caso, addtional batter
les may be needed. Using a diferent buzzer
docs not affect the tuned elreut 9 the 201)
Ant variable espacitor need not be altered
Tr the sound feor the buzzer is too loud
for the strength of its tore to bo distin
guished easily inthe speaker, enctosing
fsther the buzzer or the entire generator
in 3 cotton-padited cardboard or wooden
‘box (rot metal) will decrease the sound
foming directly from the buczer without
flcturbing the 22. cutput
if a short antenna is connected to point
(A) in the wiring dlegram, this litto egnal
generator will make an ideal code practice
Oscillator, since its signals can be transmit
ted fom one room to another without wires
‘and ean be picked up On any broadcast set!
‘The antenna should be no longer Gian neo
fexsary to profuco a good tone in tho epeaic.
fer when the reeelvers volume control 1s
‘Well tured up. When using the gencrator
In this manner, conneet the tolegranh Key
In place of the switsh shown in the dh
‘gear.
Wiring schemate of te genereten, For de